Internet Explorer's documentation states that this element should allow %core%,
%events% and %language% general attributes, but in practice (5.0 Beta 2) it does
not.
Internet Explorer 5.0 Beta 2: Using block elements in the Ruby
Base places the Ruby Text content BELOW the Ruby Base. This does not seem
to be the intention of the implementation of Rubies, so the behavior may change by
the final release.